Summary of Significant Accounting Policies - Summary of Reflection of New Adopted Standards in Selected Consolidated Statement of Cash Flow (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net income	$ 41,160	$ 33,694
Deferred income taxes, net	4,272	1,285
Deferred contract costs	(17,712)	(13,563)
Stock-based compensation expense	23,222	3,343
Net cash provided by operating activities	$ 57,664	40,225
As Previously Reported [Member]
Cash flows from operating activities
Net income		25,614
Deferred income taxes, net		(4,480)
Stock-based compensation expense		3,625
Net cash provided by operating activities		40,225
Adjustments [Member]
Cash flows from operating activities
Net income		8,080
Deferred income taxes, net		5,765
Deferred contract costs		(13,563)
Stock-based compensation expense		$ (282)